// top-level spec
export const SPEC = "spec";

// literal values
export const LITERAL = "literal";

// dataset identifier
export const DATAREF = "dataref";

// options object
export const OPTIONS = "options";

// params and selections
export const SELECTION = "selection";
export const PARAMREF = "paramref";
export const COLUMPARAMREF = "columnparamref";
export const PARAM = "param";
export const INCLUDE = "include";

// param and selection types
export const SELECT = "select";
export const VALUE = "value";
export const CROSSFILTER = "crossfilter";
export const INTERSECT = "intersect";
export const UNION = "union";
export const SINGLE = "single";

// data definitions
export const DATA = "data";

// sql expressions
export const EXPRESSION = "expression";
export const SQL = "sql";

// inputs
export const INPUT = "input";

// layout
export const HCONCAT = "hconcat";
export const VCONCAT = "vconcat";
export const HSPACE = "hspace";
export const VSPACE = "vspace";

// vgplot
export const MARK = "mark";
export const FROM = "from";
export const PLOT = "plot";
export const LEGEND = "legend";
export const ATTRIBUTE = "attribute";
export const TRANSFORM = "transform";
export const WINDOW_FRAME = "windowframe";
export const INTERACTOR = "interactor";
export const FIXED = "Fixed";
